Portable battery back-up data cartridges are commonly used for recording and transferring data between host computers, and more particularly between a field host computer and a base host computer.
An example of a computer system involving a field computer and a base computer with a data cartridge transferring information between the field and the base computers is given in U.S. Pat. No. 4,258,421 (Juhasz et al.), wherein a vehicle monitoring and recording system is disclosed. In such an environment, where the data recorded on the data cartridges includes parameters which undergo continuous updating (such as distance, fuel consumption, speed, RPM, battery voltage, oil pressure, fuel filter, cooling pressure, air pressure, brake temperature, cooling temperature, fuel temperature, and oil coolant level), it is important that the update of the data on the data cartridge be completed before the data cartridge is disconnected. In the case of an environment such as the cab of a semi-trailer truck, the data cartridge may be disconnected at any random time and it is important to prevent a partial update of the data contained on the data cartridge, as this can produce inconsistencies in the data recorded thereon.
Previous data cartridges concerned themselves with protecting the information which was being written at the moment of physical disconnection, by using connector pins that disconnected in a fixed mechanical sequence. For example, shorter pins which are disconnected first provide an early warning signal that a disconnection is imminent. It is also known that once the advent of a power failure is detected, means can be provided to switch to a battery backup power supply for keeping the memory in the cartridge alive while disconnected. An example of such a cartridge memory protection system is described in U.S. Pat. No. 4,607,351 (Gerber et al.).
Previous data cartridges do not concern themselves with the fact that multiple-byte records may be required to update the data structure held in the cartridge memory.
It is also important in computer processing environments, where the keeping of an accurate clock time is important, that the updating of real time clocks used in the field host computers be updated consistently with respect to the base host computers. The prior art data cartridges do not provide for the inclusion of a real time clock that can be utilized for field system real time clock updating, where the field system is able to select the freshest or most accurate time presented to it by any one of several cartridges presented to it.